speed and energy?
A flywheel is a solid disk that rotates about an axis that is perpendicular to the disk at its center. Rotating flywheels provide a means for storing energy in the form of rotational kinetic energy and are being considered as a possible alternative to batteries in electric cars. The gasoline burned in a 280-mile trip in a typical midsize car produces about 1.3 multiplied by 109 J of energy. How fast would a 18-kg flywheel with a radius of 0.23 m have to rotate in order to store this much energy? Give your answer in rev/min.
705,680 rpm
energy = 1/2 * I * omega^2
I = moment of inertia = 1/2 M r^2 = 1/2 * 18 * 0.23^2 = 0.476 kg m^2
energy = 1.3 x 10^9 J
so,
1.3 x 10^9 = 1/2 * 0.476 * omega^2
therefore
omega = 73906 rad/sec -> f = 11762 rev/sec = 705,680 rev/min
cheers
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